Studies on Electromagnetic Induction in the Earth:
Recent advances and Future Directions

Editorial Board (December 2021)
Editor-in-Chief
Takeshi Sagiya, Nagoya University, Japan

Vice Editors-in-Chief
Masahito Nosé, Nagoya University, Japan

Aitaro Kato, University of Tokyo, Japan

Editors
Hideo Aochi
Pascal Audet
Kiyoshi Baba
Joseph B.H. Baker
Nanan Balan
Stephan Christoph Buchert
Sonia CalvariPeter Chi
Harold C. Connolly Jr
Phil Cummins
Hao Dong
Guangyu Fu
Hidenori Genda
Aditya Gusman
Tomasz Hadaś
Shin-Chan Han
Stuart Henrys
James Hickey
Hauke Hussmann

Mie Ichihara
Takeo Ito
Hidekatsu Jin
Art Jolly
Shunichi Kamata
Nobuki Kame
Yoko Kebukawa
Kunihiro Keika
Tomokazu Kobayashi
Kostas Konstantinou
Alexey Kuvshinov
Juanjo Ledo
Atsuko Namiki
Yasuhito Narita
Kazunari Nawa
Hiroyo Ohya
Duggirala Pallamraju
Severine Rosat
Akinori Saito

Tatsuhiko Saito
David Shelly
Hisayoshi Shimizu
Hiroko Sugioka
Wataru Suzuki
Youichiro Takada
Sunny Tam
Naoki Uchida
Yanbin Wang
Yih-Min Wu
Chuang Xuan
Takahiro Yamamoto
Yuhji Yamamoto
Tadashi Yamasaki
Tatsuhiro Yokoyama
Kazunori Yoshizawa
Yohei Yukutake
Seiji Zenitani

Hiroo Kanamori
Jun'ichiro Kawaguchi
Takafumi Matsui
Hitoshi Mizutani

Yasuo Ogawa
Toshitaka Tsuda
Zhongliang Wu
Kiyoshi Yomogida

Advisory Board
Benjamin Fong Chao
Bernard Chouet
Yoshimori Honkura
Toshihiko Iyemori

Journal Scope
Earth, Planets and Space (EPS) is the official journal of Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
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Earth, Planets and Space(2021) 73:19
Bedrosian et al. Earth, Planets and Space
https://doi.org/10.1186/s40623-020-01336-6

Open Access

PREFACESpecial issue “Studies on electromagnetic
induction in the earth: recent advancesand future directions”
Paul A. Bedrosian1*, Gerhard Schwarz2, Kate Selway3, Pierre Wawrzyniak4 and Dikun Yang5

resistivity model images zones of elevated upper-crustal
conductivity coincident with surface faulting and seismicity; they interpret these zones to mark suture zones
within the Central Asian Orogenic Belt. The authors further image a distinct zone of lower-crustal conductivity
in part of the model and suggest this conductor may berelated to an exotic terrane speculated from geochemical data to exist in the same region. Finally, a step inlithospheric thickness is interpreted beneath Southern
Mongolia from the model.
The emergence of national-scale MT initiatives overthe last two decades has led to an explosion in the number of three-dimensional (3D), tectonic-scale resistivity models presented and published. Thiel et al. (2020)
present one such model, describing MT modeling of theAustralian Musgrave province based upon data collected
as part of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP). They present a 3D resistivity model of the lithosphere, arguing that conductive
structures within the model reflect tectono-magmatic
processes associated with the reworking of the Australiancontinent, including the amalgamation of cratonic components and deformation during younger orogenies.
3D resistivity models, such as the study by Thiel et al.
(2020), rely upon complex inversion algorithms withconsiderable flexibility with regard to model discretization and regularization, the choice of start and priormodels and the treatment of data and errors. Robertson
et al. (2020) present a model-space exploration of the
3D inversion ModEM3DMT (Egbert and Kelbert 2012;
Kelbert et al. 2014) using for their testbed a subset ofdata collected as part of AusLAMP. The authors investigate the influence of model covariance, the prior model,

The research community that studies electromagnetic(EM) induction in the Earth and planets continues togrow. The breadth of EM research has expanded wellbeyond the traditional focus on magnetotellurics (MT) to
include airborne, land, and marine controlled-source EM.
Advancements in the processing, modeling, inversion
and interpretation of EM data have accompanied thisgrowth and led to an increased visibility of EM researchwithin the Earth science community. The biennial workshops on Electromagnetic Induction in the Earth, first
held in 1972, continues to be the premier event for thevibrant international community of EM researchers.
The 24th workshop on Electromagnetic Induction in
the Earth was held in Helsingør, Denmark, from August
13–20, 2018. More than 330 presentations were given
spanning a range of topics including (1) instrumentation,
sources and data processing; (2) EM theory, modelingand inversion; (3) exploration, monitoring and hazards;(4) tectonics, magmatism and geodynamics; (5) marineEM; (6) rock/mineral resistivity and anisotropy; (7) global
and planetary studies and (8) EM induction educationand outreach. This special issue presents a compilation of 10 papers, described below, that highlight recent
advances and future directions within the EM researchcommunity.
Investigations of crustal and lithospheric architecture continue to be a mainstay of MT studies. Comeau
et al. (2020) present a study of the tectonic terranes ofMongolia based upon a 350-km-long MT profile. Their*Correspondence: pbedrosian@usgs.gov
1
U.S. Geological Survey, Denver, CO, USA
Full list of author information is available at the end of the article© The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material
in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material
is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds thepermitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativeco
mmons.org/licenses/by/4.0/.

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Studies on Electromagnetic Induction in the Earth: Recent advances and Future Directions
Bedrosian et al. Earth, Planets and Space(2021) 73:19

Page 2 of 3(2020) present a case study in Australia where a dense
MT data set is combined with limited well-log data toresolve basin layering and the basement interface. The
authors undertook a synthetic modeling exercise based
upon well-log data, considering both deterministic andstochastic inversions. After examining uncertainty within
the synthetic study, the authors apply their approachto map geologic interfaces and their associated errors
throughout a broad region. The authors approach provides a practical workflow for handling model uncertainty
in areas with limited independent geologic constraints.
MT data are increasingly collected in areas impacted
by infrastructure, where non-MT signals dominate measured time-series and can lead to severe degradation of
estimated MT responses. A variety of approaches to signal–noise separation operate in the time, frequency, or
wavelet domains, but most have difficulty when noiseis spatially coherent across broad regions or when datafrom a reference station is not available. Li et al. (2020)
present a machine-learning algorithm for removing noisefrom MT data contaminated by persistent or coherent
noise. The authors present their improved shift-invariant
sparse coding (ISISC) method and apply it to synthetic
data contaminated with either pseudo-random squarewave or impulsive noise sources. They demonstrate theperformance and effectiveness of the ISISC algorithm,
applying their approach to real MT data sets contaminated with controlled-source EM noise and unknown
non-MT noise. This data-driven approach offers an
attractive possibility for removing complex periodic noise
signals (e.g., pipeline signals) from MT data and pushes
the applicability of MT closer to urban areas.
Other sources of MT noise are unique to the seafloor
environment. Motion-induced EM signals due to seafloor currents are a common source of noise plaguingseafloor measurements. Chen et al. (2020) describe an
adaptive-correlation filter which incorporates seafloor
current-meter data as a reference signal in order toreduce motion-induced noise in marine MT data. The
authors demonstrate the effectiveness of their approachon time-series collected over a region near the edge ofthe continental-shelf with strong seafloor currents as wellas in a marine basin with weaker currents. Within theformer environment, their results highlight the effectiveness of the approach in producing stable MT responses
that are not seen using traditional MT processing. Given
the increased use of ocean-bottom EM receivers, thisadvance may lead to considerable improvements in thequality of processed seafloor responses.
Moving from the seafloor to air, Baranwal et al. (2020)
present an interpretation of airborne electromagnetic(AEM) data collected over the Mesozoic Ramså Basinin Norway. Their AEM models, derived from a spatiallycell size and the choice of inverted data—evaluating theresults both in terms of data misfit and model structure.
Their results suggest a practical workflow for 3D inversion and for assessing the resultant models.
Rivera-Rios et al. (2019) demonstrate the functionality of a new 3D vector finite-element forward modelingalgorithm, MoVFEM. The authors validate their algorithm against analytic or accepted numerical solutions
for a number of complex models, including a 3D community model, a halfspace model with topography and ahalfspace model with transverse anisotropy. The authors’
results demonstrate the capabilities of the MoVFEM software and hint at future modifications to incorporate the
MoVFEM algorithm within adaptive-mesh strategies.
Also on the modeling front, a study of interstation MT
impedance responses, calculated from magnetic- andelectric-field data recorded at different locations, is presented by Martí et al. (2020). The authors compare models resulting from inversion of local, interstation and‘quasi-MT’ (modeling of interstation response as if they
were local) responses for two synthetic fault models andfind that inversions of the quasi-MT responses do not
fully reproduce the synthetic structure but provide generally valid models. The authors subsequently apply thisapproach to measured data across a seismogenic fault
in Spain, identifying a prominent fault-zone conductor.
Given the reality of missing or bad data channels, interstation MT responses are sometimes all that are available.
In this context, the authors’ findings provide reassurance
that interstation responses can be reliably used within a
traditional inversion approach.
MT inversions also typically assume data errors areuncorrelated by specifying data variances, but not covariances, within the inversion. Guo et al. (2019) investigate
the impact of this assumption using a one-dimensionaltrans-dimensional Bayesian inversion approach. The
approach is applied to both synthetic and measured dataand in each case the authors compare inversions with andwithout data-error correlations. In the synthetic example,
they demonstrate that ignoring data-error correlation has
a tendency to overfit the data and underestimate model
parameters uncertainty; the ability to recover model
structure is also shown to suffer as data-error covarianceincreases. Applied to measured data, however, the model
results are nearly identical, suggesting a weak correlation
between data errors.
Quantification of uncertainty within MT resistivity
models, particularly applied to interpreted boundaries
such as depth-to-basement or stratigraphic layering, ischallenging given the non-uniqueness of the geophysicalinverse problem, the differential resolution of conductive
and resistive interfaces and the impacts of regularizationon the resulting inverse model. Simpson and Heinson

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Bedrosian et al. Earth, Planets and Space(2021) 73:19

Page 3 of 3

constrained inversion approach, compare favorably toborehole logging data as well as a number of electricalresistivity tomography profiles. The authors find that the
conductivity of pore waters has a significant impact on
the bulk resistivity within both the rocks of the sedimentary basin and the basement. The AEM models are used
to refine the extent of the Ramså Basin. Additionally, apair of conductive zones also identified within the models are tied to a graphite and sulfide-bearing outcrop.

zones across Southern Mongolia detected with a 2-dimensional magnetotelluric transect. Earth Planets Space 72:5. https://doi.org/10.1186/
s40623-020-1131-6
Egbert GD, Kelbert A (2012) Computational recipes for electromagnetic
inverse problems. Geophys J Int. 189:251–267. https://doi.org/10.1111/
j.1365-246X.2011.05347.x
Guo R, Liu L, Liu J, Sun Y, Liu R (2019) Effect of data error correlations on transdimensional MT Bayesian inversions. Earth Planets Space 71:134. https://doi.org/10.1186/s40623-019-1118-3
Kelbert A, Meqbel N, Egbert GD, Tandon K (2014) ModEM: A modular system
for inversion of electromagnetic geophysical data. Comput Geosci.
66:40–53. https://doi.org/10.1016/j.cageo.2014.01.010
Li G, Liu X, Tang J, Deng J, Hu S, Zhou C, Chen C, Tang W (2020) Improved shiftinvariant sparse coding for noise attenuation of magnetotelluric data.
Earth Planets Space 72:45. https://doi.org/10.1186/s40623-020-01173-7
Martí A, Queralt P, Marcuello A, Ledo J, Rodríguez-Escudero E, Martínez-Díaz
JJ, Campanyà J, Meqbel N (2020) Magnetotelluric characterization of theAlhama de Murcia Fault (Eastern Betics, Spain) and study of magnetotelluric interstation impedance inversion. Earth Planets Space 72:16. https://doi.org/10.1186/s40623-020-1143-2
Rivera-Rios AM, Zhou B, Heinson G, Krieger L (2019) Multi-order vector finite
element modeling of 3D magnetotelluric data including complex geometry and anisotropy. Earth Planets Space 71:92. https://doi.org/10.1186/
s40623-019-1071-1
Robertson K, Thiel S, Meqbel N (2020) Quality over quantity: on workflow andmodel space exploration of 3D inversion of MT data. Earth Planets Space
72:2. https://doi.org/10.1186/s40623-019-1125-4
Simpson JM, Heinson G (2020) Synthetic modelling of downhole resistivity
data to improve interpretation of basin morphology from magnetotelluric inversion. Earth Planets Space 72:69. https://doi.org/10.1186/s4062
3-020-01178-2
Thiel S, Goleby BR, Pawley MJ, Heinson G (2020) AusLAMP 3D MT imagingof an intracontinental deformation zone Musgrave Province, Central
Australia. Earth Planets Space 72:98. https://doi.org/10.1186/s40623-02001223-0

Acknowledgements
We wish to thank all the authors who contributed to this special issue as wellas the numerous reviewers whose comments and suggestions improved themanuscripts.
Author details
1
U.S. Geological Survey, Denver, CO, USA. 2 Geological Survey of Sweden,
Uppsala, Sweden. 3 Macquarie University, Sydney, Australia. 4 French Geological Survey, Orléans, France. 5 Southern University of Science and Technology,
Shenzhen, China.
Received: 8 December 2020 Accepted: 9 December 2020

References:
Baranwal VC, Brönner M, Rønning J-S, Elvebakk H, Dalsegg E (2020) 3D interpretation of helicopter-borne frequency-domain electromagnetic (HEM)
data from Ramså Basin and adjacent areas at Andøya, Norway. Earth
Planets Space 72:52. https://doi.org/10.1186/s40623-020-01177-3
Chen K, Zhao Q, Deng M, Luo X, Jing J (2020) Seawater motion-induced
electromagnetic noise reduction in marine magnetotelluric data using
current meters. Earth Planets Space 72:4. https://doi.org/10.1186/s4062
3-019-1129-0
Comeau MJ, Becken M, Käufl JS, Grayver AV, Kuvshinov AV, Tserendug S, Batmagnai E, Demberel S (2020) Evidence for terrane boundaries and suture

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

3Studies on Electromagnetic Induction in the Earth: Recent advances and Future Directions

FULL PAPER

Open Access

Effect of data error correlations on trans-dimensional MT
Bayesian inversions
Rongwen Guo, Liming Liu, Jianxin Liu, Ya Sun and Rong Liu*
Earth, Planets and Space 2019, 71:134 DOI: 10.1186/s40623-019-1118-3
Received: 23 April 2019, Accepted: 25 November 2019, Published: 5 December 2019

Abstract
Real magnetotelluric (MT) data errors are commonly correlated, but MT inversions routinely neglect such correlations without an
investigation on the impact of this simplification. This paper applies a hierarchical trans-dimensional (trans-D) Bayesian inversion
to examine the effect of correlated MT data errors on the inversion for subsurface geoelectrical structures, and the model
parameterization (the number of conductivity interfaces) is treated as an unknown. In the inversion considering error
correlations, the data errors are parameterized by the first-order
autoregressive (AR(1)) process, which is included as an unknown in the
inversion. The data information itself determines the AR(1) parameter. The
trans-D inversion applies the reversible-jump Markov chain Monte Carloalgorithm to sample the trans-D posterior probability density (PPD) for themodel parameters, model parameterization and AR(1) parameters,
accounting for the uncertainties of the model dimension and data error
correlation in the uncertainty estimates of the conductivity profile. In the
inversion ignoring the correlation, we neglect the correlation effect byturning off the AR(1) parameter. Then the correlation effect on the MT
inversion can be examined upon comparing the posterior marginal
conductivity profiles from the two inversions. Further investigation is thencarried out for a synthetic case and a real MT data example. The results
indicate that for strong correlation cases, neglecting error correlations cansignificantly affect the inversion results.

Keywords: Trans-D Bayesian inversion, Autoregressive model,
Parameterization, Magnetotelluric method

Graphical abstract*Corresponding author: Rong Liu, liurongkaoyan@126.com

FULL PAPER

Open AccessQuality over quantity: on workflow and model space
exploration of 3D inversion of MT data
K. Robertson*, S. Thiel and N. Meqbel
Earth, Planets and Space 2020, 72:2 DOI: 10.1186/s40623-019-1125-4
Received: 5 August 2019, Accepted: 18 December 2019, Published: 7 January 2020

Abstract
3D inversions of magnetotelluric data are now almost standard, with computational power now allowing an inversion to be
performed in a matter of days (or hours) rather than weeks. However, when compared to 2D inversions, these are still very
computationally demanding. As a result, 3D inversions are generally not subjected to as rigorous testing as a 1D or 2D inversion
would be, which has implications when these models are used for geological interpretation. In this study, we explore theparameter space for inversion of continent-scale datasets. The generalisations made regarding the effects of each parametershould also be scalable to smaller surveys and will enable MT practitioners to optimise their results. We have performed testing
on a subset of the South Australian component of the eventual Australia-wide AusLAMP (Australian Lithospheric Architecture
Magnetotelluric Project). The subset was inverted with different
parameters, model setup and data subsets. Specifically, results fromtesting of the model covariance, the resistivity of the prior model, theinclusion of 'known' information into the prior model, the model cellsize, the data components inverted for and the damping parameter lwere all investigated. In our testing of the 3D inversion software,
ModEM3DMT, we found that the resistivity of the starting/priormodel had significant effect on the final model. Careful selection of
initial l value can aid in reducing computational time whilst having anegligible effect on the resultant model, whilst large covariancevalues and model cell sizes enhanced conductive features at depth.

Keywords: Magnetotellurics, 3D inversion, AusLAMP, Electricalresistivity, ModEM3DMTGraphical abstract*Corresponding author: K. Robertson, Kate.Robertson2@sa.gov.au
4

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Open Access

Seawater motion-induced electromagnetic noise reduction
in marine magnetotelluric data using current meters
Kai Chen*, Qingxian Zhao, Ming Deng, Xianhu Luo and Jianen Jing
Earth, Planets and Space 2020, 72:4 DOI: 10.1186/s40623-019-1129-0
Received: 11 February 2019, Accepted: 26 November 2019, Published: 13 January 2020

Abstract
Seawater motion-induced electromagnetic (EM) noise along the seafloor has a large impact on marine magnetotelluric (MT) data
quality. Although the mechanical stability of ocean bottom electromagnetic receivers (OBEMs) has improved due to buoyancy
optimization, completely eliminating EM noise generated by seafloor currents as a result of instrument rocking or induction fromthe Earth’s magnetic field is still not possible. The velocity of the current represents the quantification of seafloor conditions. To
mitigate this problem, we installed a current meter on an OBEM to measure the synchronous current velocity along with the
OBEM data logger. For the marine EM surveys, we conducted two surveys composed of 42 marine EM data acquisition sites in theSouth China Sea. We observed a strong correlation between induced EM noise and current velocity when the speed was greaterthan 2 cm/s. Furthermore, we developed an adaptive correlationnoise-canceling filter to reduce the induced EM noise, using thecurrent meter data as a reference signal. The filter refined thecoefficients using a least-mean-squares algorithm. We were able toreduce the induced EM noise by pre-filtering the raw time series datawith an adaptive correlation noise-canceling filter and using current
meter data from nearby sites. Since seafloor currents are clearly an
issue that limits MT data quality, special efforts are necessary to
reduce seawater motion-induced EM noise in marine MT surveys.

Keywords: Marine magnetotelluric, Adaptive correlationnoise-canceling filter, Seawater motion-induced
electromagnetic noise, Current meter

Graphical abstract*Corresponding author: Kai Chen, ck@cugb.edu.cn

FULL PAPER

Open Access

Evidence for terrane boundaries and suture zones across Southern Mongolia
detected with a 2-dimensional magnetotelluric transect
Matthew J. Comeau*, Michael Becken, Johannes S. Käufl, Alexander V. Grayver, Alexey V. Kuvshinov,Shoovdor Tserendug, Erdenechimeg Batmagnai and Sodnomsambuu Demberel
Earth, Planets and Space 2020, 72:5 DOI: 10.1186/s40623-020-1131-6
Received: 28 June 2019, Accepted: 7 January 2020, Published: 16 January 2020

Abstract
Southern Mongolia is part of the Central Asian Orogenic Belt, the origin and evolution of which is not fully known and is often debated. It is
composed of several east–west trending lithostratigraphic domains that are attributed to an assemblage of accreted terranes or tectonic zones. This
is in contrast to Central Mongolia, which is dominated by a cratonic block in the Hangai region. Terranes are typically bounded by suture zones thatare expected to be deep-reaching, but may be difficult to identify based on observable surface fault traces alone. Thus, attempts to match
lithostratigraphic domains to surface faulting have revealed some disagreements in the positions of suspected terranes. Furthermore, the subsurface
structure of this region remains relatively unknown. Therefore, high-resolution geophysical data are required to determine the locations of terraneboundaries. Magnetotelluric data and telluric-only data were acquired across Southern Mongolia on a profile along a longitude of approximately
100.5° E. The profile extends ~ 350 km from the Hangai Mountains, across the Gobi–Altai Mountains, to the China–Mongolia border. The data wereused to generate an electrical resistivity model of the crust and upper mantle, presented here, that can contribute to the understanding of thestructure of this region, and of the evolution of the Central Asian Orogenic Belt. The resistivity model shows a generally resistive upper crust (0–20km) with several anomalously conductive features that are believed to indicate suture zones and the boundaries of tectonic zones. Moreover, their
spatial distribution is coincident with known surface fault segments and active seismicity. The lower crust (30–45 km) becomes generally lessresistive, but contains an anomalously conductive feature below the Gobi–Altai
zone. This potentially agrees with studies that have argued for an
allochthonous lower crust below this region that has been relaminated andmetamorphosed. Furthermore, there is a large contrast in the electricalproperties between identified tectonic zones, due to their unique tectonic
histories. Although penetration to greater depths is limited, themagnetotelluric data indicate a thick lithosphere below Southern Mongolia, incontrast to the previously reported thin lithosphere below Central Mongolia.

Keywords: Magnetotellurics, Electrical resistivity, Southern Mongolia,
Gobi, Terranes, Suture zones*Corresponding author: Matthew J. Comeau, matthew.comeau@uni-muenster.de
5Graphical abstract

Studies on Electromagnetic Induction in the Earth: Recent advances and Future Directions

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Open Access

Magnetotelluric characterization of the Alhama de Murcia
Fault (Eastern Betics, Spain) and study of magnetotelluric interstation
impedance inversion
Anna Martí*, Pilar Queralt, Alex Marcuello, Juanjo Ledo, Emilio Rodríguez-Escudero,
José Jesús Martínez-Díaz, Joan Campanyà and Naser Meqbel
Earth, Planets and Space 2020, 72:16 DOI: 10.1186/s40623-020-1143-2
Received: 29 June 2019, Accepted: 22 January 2020, Published: 10 February 2020

Abstract
The Lorca earthquake (May 11th, 2011, Mw 5.2) stands as the most destructive one in Spainover the last 50 years, interpreted as having occurred in an intersegment zone of the strike–slip Alhama de Murcia Fault (AMF) (Eastern Betics, Spain). Magnetotelluric data wereacquired along a profile to the SW of Lorca (La Torrecilla profile), to characterize its signature
at depth, as part of the multidisciplinary project “INTERGEOSIMA”. Given the short distance
between stations, some station pairs were recorded simultaneously, with magnetic sensors
in only one of them. In order to properly understand the resulting impedances (calledinterstation impedances), and the effects of inverting them, we used synthetic models tocompare the impedances and the interstation impedances and to analyze thecorresponding inversion results, together with the inversion of the quasi-impedance(inversion of the interstation impedances, considering them as impedances). The results
are sensitive to the location of the magnetic sensors and the resistivity underneath, but ingeneral the use of the quasi-impedances in the inversion can be considered a valid
procedure. Both the 2D and the 3D resistivity models obtained through the inversion
allowed us to complement the previous ERT models and represent the continuation of themain fault gouge in depth showing its extension towards the SE.

Keywords: Magnetotellurics, Alhama de Murcia Fault, Interstation impedance inversion

Graphical abstract*Corresponding author: Anna Martí, annamarti@ub.edu

FULL PAPER

Open Access

Improved shift-invariant sparse coding for noise attenuationof magnetotelluric data
Guang Li, Xiaoqiong Liu, Jingtian Tang, Juzhi Deng, Shuanggui Hu*, Cong Zhou*, Chaojian Chen
and Wenwu Tang
Earth, Planets and Space 2020, 72:45 DOI: 10.1186/s40623-020-01173-7
Received: 6 July 2019, Accepted: 28 March 2020, Published: 6 April 2020

Abstract
Magnetotelluric (MT) method is widely used for revealing deep electrical structure. However, natural MT signals are susceptible
to cultural noises. In particular, the existing data-processing methods usually fail to work when MT data are contaminated bypersistent or coherent noises. To improve the quality of MT data collected with strong ambient noises, we propose a novel
time-series editing method based on the improved shift-invariant sparse coding (ISISC), a data-driven machine learningalgorithm. First, a redundant dictionary is learned autonomously from the raw MT data. Second, cultural noises are reconstructedusing the learned dictionary and the orthogonal matching pursuit (OMP) algorithm. Finally, the de-noised MT data are obtainedby subtracting the reconstructed cultural noises from the raw MT data. The synthetic data, field experimental data and measured
data are tested to verify the effectiveness of the newly proposed method. The results show that our new scheme can effectively
remove strong cultural noises and has
better adaptability and efficiency than thepredefined dictionary-based methods. The
method can be used as an alternative whena remote reference station is not available.

Keywords: Magnetotelluric, Machinelearning, Shift-invariant sparse
coding (SISC), De-noising,
Dictionary learning

Graphical abstract*Corresponding author: Shuanggui Hu, hushuanggui808@csu.edu.cn; Cong Zhou, zhoucong_522@163.com
6

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Open Access

3D interpretation of helicopter-borne frequency-domain
electromagnetic (HEM) data from Ramså Basin and adjacentareas at Andøya, Norway
Vikas Chand Baranwal*, Marco Brönner, Jan-Steinar Rønning, Harald Elvebakk and Einar Dalsegg
Earth, Planets and Space 2020, 72:52 DOI: 10.1186/s40623-020-01177-3
Received: 8 July 2019, Accepted: 15 April 2020, Published: 28 April 2020

Abstract
The Ramså Basin is situated on the strandflat on the northeastern side of Andøya between Ramså andSkarstein. It is the only known Mesozoic sedimentary basin onshore Norway and therefore represents
an easily accessible analogue to study the setting and development of the offshore Mesozoic basins
along the Norwegian continental shelf. Basement rocks (100–10,000 Ωm) and sedimentary rocks(5–1000 Ωm) have distinct ranges of the electrical resistivity. Resistivity of the subsurface can beinvestigated by electric and electromagnetic (EM) methods to delineate the extent of the sedimentarybasin. This paper presents the interpretation of helicopter-borne frequency-domain electromagnetic(HEM) data and their correlation with data obtained from borehole logging and two-dimensional (2D)electrical resistivity tomography (ERT). Resistivity data obtained from these methods show a good
agreement. Spatially constrained inversion (SCI) of HEM presents a three-dimensional (3D) subsurface
resistivity image of a larger area in comparison to what could have been drawn from few ERT lines andborehole logging. HEM interpretation together with other ERT and borehole resistivity data indicatesthe extent of Ramså Basin beyond the presently mapped boundary. This extension is also supported byinterpretation of earlier collected gravity, magnetic and seismic data. The Ramså sedimentary basinshows a wide range of electrical resistivity between ca. 10 and 600 Ωm at different depths. Two highly
conductive areas are newly identified by HEM data interpretation. In one of these areas, outcropping
graphite and sulfide minerals were found by field observations.

Keywords: Airborne EM, Ramså Basin, Frequency-domain helicopter-borne electromagnetic (HEM),
Spatially constrained inversion (SCI), Mesozoic bedrock

Graphical abstract*Corresponding author: Vikas Chand Baranwal, Vikas.Baranwal@ngu.no

FULL PAPER

Open Access

Synthetic modelling of downhole resistivity data to improve
interpretation of basin morphology from magnetotelluric
inversion
Janelle M. Simpson* and Graham Heinson
Earth, Planets and Space 2020, 72:69 DOI: 10.1186/s40623-020-01178-2
Received: 14 June 2019, Accepted: 15 April 2020, Published: 14 May 2020

Abstract
Prospective Proterozoic units in the southern Mount Isa Province are concealed by a poorly defined extent of younger basin cover, leading to poor
exploration success. Collection of a magnetotelluric (MT) survey in the area containing 809 broadband MT (BBMT) and 855 audiomagnetotelluric(AMT) stations in 2014–2015, offers an opportunity to better model the depth to basement to enable effective exploration. MT inversion models are
inherently non-unique, requiring independent geophysical and geological constraint to reduce model uncertainty. Where data are not available toconstrain inversion, alternative approaches to dealing in inversion variability are required. This study uses synthetic modelling based on well data
combined with two kinds of inversion to generate an interpretation and quantify associated uncertainty. Downhole resistivity logs were obtained
from three petroleum wells adjacent to the study area, and 1D resistivity models were generated from the downhole data. A suite of 1D and 2D MT
inversion algorithms were tested to determine their ability to resolve basin layering and the basement interface. All inversion algorithms reproduced
basin layering, but the basement interface was poorly resolved. A combination of Occam2D and 1D rjMcMC inversions were used to produce
interpretation of the base of the Eromanga Basin, an intra-Georgina Basin low-resistivity layer and depth to basement, all of which have associatederror estimates. This work highlights the importance of understanding inversion
variability during interpretation of geological features, particularly in theabsence of constraining information. Distribution of uncertainty between theinterpretation features is significantly non-uniform, necessitating carefulconsideration of inversion results. By quantifying uncertainty rather thanignoring it, we produce an interpretation commensurate with data limitations
that still provides valuable new information about the geology of the southern
Mount Isa Province.

Keywords: Depth to basement, Magnetotelluric inversion, Synthetic

modelling, Uncertainty quantification, Mount Isa Province,
Georgina Basin, Eromanga Basin*Corresponding author: Janelle M. Simpson, janelle.simpson@dnrme.qld.gov.au
7Graphical abstract

Studies on Electromagnetic Induction in the Earth: Recent advances and Future Directions

FULL PAPER

Open Access

AusLAMP 3D MT imaging of an intracontinental deformation
zone, Musgrave Province, Central Australia
Stephan Thiel*, Bruce R. Goleby, Mark J. Pawley and Graham Heinson
Earth, Planets and Space 2020, 72:98 DOI: 10.1186/s40623-020-01223-0
Received: 8 July 2019, Accepted: 27 June 2020, Published: 11 July 2020

Abstract
The central Australian Musgrave Province at the junction of the South, North and West Australian cratons has undergone and continues to retain
evidence of significant whole-of-crust, and most likely ‘whole-of-lithosphere’ tectono-magmatic processes. The area is known for some of thelargest geophysical anomalies related to significant Moho offsets of up to 15 km, which resulted from repeated intracratonic reworking since the
Neoproterozoic. New magnetotelluric (MT) data have been collected across the Musgrave Province in Western Australia and South Australia aspart of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP). Station spacing was ~ 50km between 96 sites over an area of
500 × 700 km. Long-period MT impedance and tipper data over a bandwidth of 8 s to 10,000 s period have been inverted using a smooth 3D
inverse algorithm. The 3D model shows two predominant resistivity trends. There are deep (>65 km) north–south mantle conductors that weinfer to be related to the Palaeo- to Mesoproterozoic north-trending arc-related
rocks that experienced ultra-high temperature metamorphism and widespreadmagmatism during the Mesoproterozoic Musgravian Orogeny. These conductors
are preserved in the crust south of the Musgrave Province. The upper mantle also
contains a localised resistive zone that possibly represents generation of mafic- toultramafic magmas during the c. 1090–1040 Ma Giles Event. The crust (<65 km
depth) contains strong east–west crustal conductors interpreted to reflect theeast–west structural grain that initiated during the c. 1090–1040 Ma Giles Eventand overprinted the older N–S-oriented mantle anomalies. These E–W crustal
conductors coincide with magnetic anomalies that represent crustal-scale
structures, and high gravity anomalies associated with significant Moho offsets
resulting from further reactivation during the c. 630–520 Ma Petermann and c.
450–300 Ma Alice Springs orogenies.

Keywords: Magnetotelluric, AusLAMP, Musgrave Province, Intraplatedeformation, Intracontinental deformation, Central Australia
Graphical abstract*Corresponding author: Stephan Thiel, stephan.thiel@sa.gov.au

TECHNICAL REPORT

Open AccessMulti-order vector finite element modeling of 3D
magnetotelluric data including complex geometry andanisotropy
Aixa M. Rivera-Rios*, Bing Zhou, Graham Heinson and Lars Krieger
Earth, Planets and Space 2019, 71:92 DOI: 10.1186/s40623-019-1071-1
Received: 22 December 2018, Accepted: 17 August 2019, Published: 29 August 2019

Abstract
We introduce MoVFEM, a computational algorithm for the modeling of three-dimensional magnetotelluric (MT) data using avector finite element method of specific order from multiple elements’ orders. Our algorithm allows complex geometries,
topography, and anisotropic resistivity structures. The software calculates secondary electric and magnetic fields for a planewave primary magnetic field. Accurate calculation of fields in the boundary regions of the computational domain are ensured by
the implementation of the Generalized Perfect
Matched Layers method. We validate the
MoVFEM algorithm by applications to various
scenarios, which allow a comparison withanalytical or accepted numerical solutions
where available. The respective results of ouralgorithm are in good agreement with existing
solutions.

Keywords: Numerical modeling, Electricalresistivity anisotropy, Finite
element method, Edge elements,
Magnetotellurics
Graphical abstract*Corresponding author: Aixa M. Rivera-Rios, rivera.aixa@gmail.com
8

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Contents
Special issue “Studies on electromagnetic induction in the earth: recent advances and future directions”................................................................................. Paul A. Bedrosian, Gerhard Schwarz, Kate Selway, Pierre Wawrzyniak and Dikun Yang
Effect of data error correlations on trans-dimensional MT Bayesian inversions.............................................................................................................................. Rongwen Guo, Liming Liu, Jianxin Liu, Ya Sun and Rong Liu
Quality over quantity: on workflow and model space exploration of 3D inversion of MT data...................................................................................................................................................................... K. Robertson, S. Thiel and N. Meqbel
Seawater motion-induced electromagnetic noise reduction in marine magnetotelluric data using current meters................................................................................................................. Kai Chen, Qingxian Zhao, Ming Deng, Xianhu Luo and Jianen Jing
Evidence for terrane boundaries and suture zones across Southern Mongolia detected with a 2-dimensional
magnetotelluric transect .............................................Matthew J. Comeau, Michael Becken, Johannes S. Käufl, Alexander V. Grayver,Alexey V. Kuvshinov, Shoovdor Tserendug, Erdenechimeg Batmagnai
and Sodnomsambuu Demberel

Magnetotelluric characterization of the Alhama de Murcia Fault (Eastern Betics, Spain) and study of magnetotelluric
interstation impedance inversion ..................Anna Martí, Pilar Queralt, Alex Marcuello, Juanjo Ledo, Emilio Rodríguez-Escudero,
José Jesús Martínez-Díaz, Joan Campanyà and Naser Meqbel

Improved shift-invariant sparse coding for noise attenuation of magnetotelluric data................................Guang Li, Xiaoqiong Liu, Jingtian Tang, Juzhi Deng, Shuanggui Hu, Cong Zhou, Chaojian Chen and Wenwu Tang
3D interpretation of helicopter-borne frequency-domain electromagnetic (HEM) data from Ramså Basin and adjacentareas at Andøya, Norway ...........................................................................Vikas Chand Baranwal, Marco Brönner, Jan-Steinar Rønning,
Harald Elvebakk and Einar Dalsegg

Synthetic modelling of downhole resistivity data to improve interpretation of basin morphology from magnetotelluric
inversion ...........................................................................................................................................Janelle M. Simpson and Graham Heinson
AusLAMP 3D MT imaging of an intracontinental deformation zone, Musgrave Province, Central Australia.............................................................................................................. Stephan Thiel, Bruce R. Goleby, Mark J. Pawley and Graham Heinson
Multi-order vector finite element modeling of 3D magnetotelluric data including complex geometry and anisotropy.................................................................................................................. Aixa M. Rivera-Rios, Bing Zhou, Graham Heinson and Lars Krieger

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Cover image: Robertson, K. et al., Earth, Planets and Space 2020, 72:2 DOI: 10.1186/s40623-019-1125-4